The debate over the fairness of high-frequency trading is heating up after the release of Michael Lewis's new book, "Flash Boys: A Wall Street Revolt." Proponents of HFT say it adds liquidity to the market, while those against the practice say it benefits the few at the expense of many.

CNBC's "Fast Money" spoke with Seth Merrin, the founder and CEO of the largest buy-side-only institutional trading network on the globe, Liquidnet.

"There are some high-frequency traders that are good and there are some that are very bad. And the ones that are bad make a lot of money at the expense of very many," he said. "They make a lot of money at the expense of all of those people that invest their money into the mutual funds and the pension funds."

However, Merrin doesn't believe high-frequency traders are entirely to blame. "You have to assign some of this blame to the SEC for approving all of the different order types that all of these exchanges use and help to facilitate this type of trading," he said.